The present invention relates generally to optical instruments, and more particularly to an apparatus for use in adjusting ocular mechanism in such instruments to effect focus thereof. Although the invention has wide utility, it has proven particularly useful in the context of focusing a telescope and is described as such herein.
A conventional telescope, it will be appreciated, is a combination of two optical systems, such systems cooperating to bring a distant object into view. The systems, namely an eyepiece and an objective, are relatively positionally adjustable via apparatus known as an optical focuser. Most commonly, the focuser is mounted to the telescope objective and the eyepiece is carried by the focuser, the eyepiece being moved relative the objective to effect telescope focus. Focus is achieved when the primary principle focal point of the eyepiece is brought into coincidence with the secondary principle focal point of the objective.
In the past, telescope enthusiasts have focused their equipment using mechanism such as a sliding drawtube, a threaded focusing tube, or a rack and pinion combination. Although effective under limited circumstances, such mechanisms necessarily require the use of components machined to within precise tolerances and are therefore costly to manufacture and difficult to maintain. Where equipment does not meet the prescribed tolerances, whether it be due to careless construction or to inevitable wear between moving parts, the telescope will be plagued by problems related to rocking, slipping or even jamming of the eyepiece. A failure to meet desired tolerances will also lead to "slop" in the relative adjustment of optical systems and therefore to difficulty in bringing the telescope into focus. It is therefore an object of this invention to provide a focuser employing improved mechanism for use in dealing with problems related to inaccurate machining or component wear.
In an attempt to deal with the above-identified problems, at least one focuser has heretofore been developed which employs a pivotally adjustable rotating shaft to effect movement of an eyepiece by operative frictional engagement therewith. Such an apparatus, known generally as a Crayford focuser, maintains operative engagement between the rotating shaft and the eyepiece via biased pivoting of the shaft. This arrangement, however, fails to deal adequately with the problem of eyepiece-adjustment slop, pivot of the rotating shaft bringing about a corresponding change in the frictional force applied to the eyepiece. The change in the direction of the applied force may, in turn, lead to an improper distribution of stresses within the focuser, and thus to excessive wear. It is therefore an object of this invention to provide a focuser which includes improved mechanism for use in addressing the problem of "slop" in eyepiece adjustment.
Another problem with known Crayford focusers relates to the inadequate protection offered to the telescope eyepiece during the focusing operation, the eyepiece usually being carried through an aperture in a generally flat base. Although the eyepiece may be carried in a movable drawtube, the drawtube moves through the aperture with limited structural support. It is therefore an object of this invention to provide a focuser which offers improved protection to the eyepiece during focusing thereof.
These and other objects, which will become apparent upon reading further, are attained by the present invention as shown in the drawings and described in the specification set forth below.